Sorption Behavior Of Substituteted Polycyclic Aromatic Hydrocarbons Onto Polystyrene Microplastics

Plastic products were widely used in human production and life due to their excellent physical and chemical properties,durability and cheapness.However,due to the massive production of plastic waste and unreasonable disposal methods,it has caused serious environmental problems.Plastic fibers,particles or fragments with a particle size of<5mm are defined as microplastics and are widely detected in the marine environment.The pollution of marine microplastics has become a new problem and challenge in global environmental pollution.More and more studies have shown that because the surface of microplastics is hydrophobic,it can have a strong sorption effect on organic pollutants,so it can be used as a carrier to absorb a large number of pollutants.The adsorbed organic pollutants may migrate in the environment or transfer to organisms along with the microplastics,thereby causing potential environmental risks and biological toxicity.At present,the research on the sorption of pollutants polycyclic aromatic hydrocarbons(PAHs)by microplastics was mainly based on the parent ring PAHs,and the sorption behavior and mechanism of its derivatives were relatively few.In order to study the influence of the number of rings,the structure of substituents and the position of substitution on the sorption of PAHs by microplastics,a microplastic that was often detected in the environment—polystyrene(PS)is selected as the research object,and 4-ring PAHs pyrene and its derivatives(1-methylpyrene,1-hydroxypyrene,1-aminopyrene and1-pyrenecarboxylic acid)and 2-ring PAHs naphthalene and its derivatives(2-methylnaphthalene,1-ethylnaphthalene,2-ethylnaphthalene,2,3-dimethylnaphthalene)are the target pollutants.The sorption characteristics and mechanism of PS microplastics on PAHs and their derivatives were studied,and the effects of different environmental factors(salinity,temperature)and particle size changes on the sorption process were analyzed.The main results are as following:Under neutral conditions,there was no obvious sorption between 1-pyrenecarboxylic acid and PS microplastics.The sorption kinetics of pyrene,1-methylpyrene,1-hydroxypyrene and 1-aminopyrene on PS microplastics could be fitted with the pseudo-second-order model,which showed that the sorption rate of PS microplastics for pyrene derivatives was greater than that for the parent ring pyrene.In addition,the sorption isotherm of pyrene and its derivatives onto PS microplastics could be fitted with a linear model.The results showed that the sorption coefficient followed the order of1-methylpyrene>pyrene>1-hydroxypyrene>1-aminopyrene.It showed that the existence of-OH and-NH₂groups hinder the sorption of pyrene derivatives on PS microplastics,while-CH₃groups promote the sorption to a certain extent.The sorption capacity of PS microplastics for pyrene and its derivatives increases with the decrease of its particle size.The influences of salinity and temperature on the sorption behavior between PS microplastics and pyrene and its derivatives were related to the substituents on the pyrene ring.The combination of experiments and theoretical calculations showed that hydrophobic interaction,?-?interaction and pore filling were the main sorption mechanisms between PS microplastics and pyrene and its derivatives.The sorption kinetics of PS microplastics on naphthalene and its derivatives could be fitted with the pseudo-second-order model.The sorption isotherm showed that the Freundlich model is suitable for describing the sorption of naphthalene and its derivatives on PS microplastics.Comparing the sorption of PS microplastics on 1-ethylnaphthalene and 2-ethylnaphthalene(with different substitution positions),the sorption capacity of2-ethylnaphthalene was much higher than that of 1-ethylnaphthalene.It was worth noting that the sorption capacity of PS microplastics for 2-substituted alkylnaphthalenes was significantly higher than that of 1-substituted,so there may be some mechanism or energy that promotes the sorption of 2-substituted alkylnaphthalenes on PS microplastics.Under neutral conditions,the electrostatic interaction between PS microplastics and naphthalene and its derivatives has little effect on sorption.As the particle size decreases,the specific surface area increases and pores appear,and the sorption amount of naphthalene and its derivatives on the PS microplastics increases.Salinity improves the sorption capacity of naphthalene and its derivatives on PS microplastics mainly through the salting-out effect.In a certain temperature range,the sorption capacity of PS microplastics on naphthalene and its derivatives increases with the increase of temperature.